Relay node and method for receiving a signal from a base station in a mobile communication system

ABSTRACT

Provided are a method for receiving information on a relay node zone and reference signals for a relay node from a base station, and a relay node device using same. The relay node can receive information on at least one start point from the start points of a Relay-Physical Downlink Control Channel (R-PDCCH) and a Relay-Physical Downlink Shared Channel (R-PDSCH) for transmitting a signal from a base station to a relay node in a specific downlink subframe. Alternatively, the relay node can implicitly recognize the start points of the R-PDCCH and R-PDSCH set in advance. The relay node can recognize a signal from the base station in the specific downlink subframe based on the start point information after the time corresponding to at least one of the start points of the R-PDCCH and R-PDSCH. Also, the relay node can decode signals transmitted from a base station after the corresponding timing.

This application is a 35 U.S.C. §371 National Stage entry ofInternational Application No. PCT/KR2010/002903, filed on May 7, 2010,and claims the benefit of U.S. Provisional Application No. 61/176,491,filed May 8, 2009, and Korean Patent Application No. 10-2010-0042766,filed May 7, 2010, each of which are hereby incorporated by reference intheir entireties as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to a mobile communication system, and moreparticularly to a method for allowing a relay node (RN) to receive asignal using information of a relay node (RN) zone allocated fordownlink (DL) transmission from an eNode B to the RN, and a method forallowing the eNode B to allocate a reference signal (RS) for the RN.

BACKGROUND ART

If a channel condition between an eNode B and the UE is poor, a relaynode (RN) is installed between the BS and the UE such that it canprovide an RF channel having superior channel conditions to the UE. Inaddition, a relay node (RN) is introduced to a cell edge region having apoor channel condition such that it can provide a higher-speed datachannel and can extend a cell service region. As described above, therelay node (RN) has been widely used to solve the propagation shaderegion in a wireless communication system.

Compared to the conventional relay node (RN) art that is restricted tofunctions of a repeater capable of amplifying/transmitting a signal, thelatest technology is being developed to cover more intelligenttechniques. Furthermore, the relay node (RN) technology can reduce costsassociated with increasing the number of eNode Bs and maintenance costsof a backhaul network in next generation mobile communication systems,and is requisite for extending the service coverage simultaneously whileincreasing the data processing rate. With the increasing development ofrelay node (RN) technology, the necessity for the relay node (RN) usedin the conventional wireless communication system to be supported by thenew wireless communication system is also increasing.

As the technology for forwarding a link connection between the eNode Band the UE is introduced to a relay node (RN) in a 3^(rd) GenerationPartnership Project Long Term Evolution-Advanced (3GPP LTE-A) system,two links having different attributes are applied to a UL carrierfrequency band and a DL carrier frequency band. The connection linkbetween the eNode B and the RN is defined as a backhaul link.Transmission of data using downlink (DL) resources according to aFrequency Division Duplexing (FDD) or Time Division Duplexing (TDD)scheme is referred to as backhaul downlink. Transmission of data usinguplink (UL) resources according to the FDD or TDD scheme is referred toas backhaul uplink.

FIG. 1 is a conceptual diagram illustrating a relay backhaul link and arelay access link for use in a wireless communication system.

Referring to FIG. 1, the RN may receive information from the eNode Bthrough a relay backhaul downlink, and may transmit information to theeNode B through a relay backhaul uplink. In addition, the relay node maytransmit information to the UE through the relay access downlink, or mayreceive information from the UE through the relay access uplink.

Although the LTE-A system evolved from the LTE system acting as a mobilecommunication system supports the RN, the RN is not aware of a specifictime at which the RN receives control information and data from theeNode B. As a result, the reception efficiency of a signal transmittedfrom the eNode B to the RN is unavoidably deteriorated.

In order to enable the LTE-A system to support the RN, a method forallocating a reference signal (RS) in a zone allocated for the RN and amethod for allocating a control channel for the RN have not beeninvestigated yet. In order to implement efficient signaltransmission/reception of the RN, there are needed a method forallocating a reference signal (RS) in an RN zone and a method forallocating a control channel for the RN.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

An object of the present invention is to provide a method for receivinga signal of a relay node (RN).

Another object of the present invention is to provide a relay node (RN)apparatus for receiving a signal from an eNode B.

It is to be understood that technical objects to be achieved by thepresent invention are not limited to the aforementioned technicalobjects and other technical objects which are, not mentioned herein willbe apparent from the following description to one of ordinary skill inthe art to which the present invention pertains.

Technical Solution

The object of the present invention can be achieved by providing amethod for receiving a signal at a relay node (RN) in a mobilecommunication system including receiving information on at least one ofstart points of a relay-physical downlink control channel (R-PDCCH) anda relay-physical downlink shared channel (R-PDSCH) that are used totransmit a signal from an eNode B to the relay node at a specificdownlink subframe; receiving a signal from the eNode B at the specificdownlink subframe based on the received start point information since aspecific time corresponding to at least one of the R-PDCH and R-PDSCHstart points; and decoding the received signal.

At least one of the R-PDCCH and R-PDSCH start points may be representedby an OFDM symbol level.

At least one of the R-PDCCH start point and the R-PDSCH start point maybe a fourth OFDM symbol in time order among a plurality of OFDM symbolsof the specific subframe.

At least one of the R-PDCCH start point and the R-PDSCH start point maybe dynamically allocated to each subframe. At least one of the R-PDCCHstart point and the R-PDSCH start point may be equally allocated to eachRN belonging to the same cell.

The specific subframe may be a fake-Multicast Broadcast Single FrequencyNetworking (fake-MBSFN) subframe.

In another aspect of the present invention, a relay node (RN) apparatusfor receiving a signal in a mobile communication system includes a radiofrequency (RF) unit configured to receive at least one of start pointsof a relay-physical downlink control channel (R-PDCCH) andrelay-physical downlink shared channel (R-PDSCH) that are used totransmit a signal from an eNode B to the relay node at a specificdownlink subframe, and receive a signal from the eNode B at the specificdownlink subframe based on the received start point information since aspecific time corresponding to at least one of the R-PDCH and R-PDSCHstart points; and a processor configured to decode the received signal.

At least one of the R-PDCCH and R-PDSCH start points may be representedby an OFDM symbol level.

At least one of the R-PDCCH and R-PDSCH start points received at the RFunit may be a fourth OFDM symbol in time order among a plurality of OFDMsymbols of the specific subframe.

At least one of the R-PDCCH start point and the R-PDSCH start point maybe dynamically allocated to each subframe. At least one of the R-PDCCHstart point and the R-PDSCH start point may be equally allocated to eachRN belonging to the same cell.

The specific subframe may be a fake-Multicast Broadcast Single FrequencyNetworking (fake-MBSFN) subframe.

Effects of the Invention

As apparent from the above description, exemplary embodiments of thepresent invention have the following effects. The relay node (RN) canefficiently decode a Relay-Physical Downlink Control Channel (R-PDCCH)start point and a Relay-Physical Downlink Shared Channel (R-PSDCH) startpoint using information regarding a RN zone in which an eNode Btransmits control information, data, etc. for the relay node (RN).

According to the embodiments of the present invention, an eNode Ballocates a reference signal (RS) according to an RS allocation methodfor channel estimation and/or demodulation of a relay node (RN), suchthat the Rn can correctly estimate a downlink (DL) channel state fromthe eNode B and at the same time can efficiently receive DL data fromthe eNode B.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved with the present invention are not limitedto what has been particularly described hereinabove and other advantagesof the present invention will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings.

Effects of the Invention

As apparent from the above description, exemplary embodiments of thepresent invention have the following effects. The relay node (RN) canefficiently decode a Relay-Physical Downlink Control Channel (R-PDCCH)start point and a Relay-Physical Downlink Shared Channel (R-PSDCH) startpoint using information regarding a RN zone in which an eNode Btransmits control information, data, etc. for the relay node (RN).

According to the embodiments of the present invention, an eNode Ballocates a reference signal (RS) according to an RS allocation methodfor channel estimation and/or demodulation of a relay node (RN), suchthat the Rn can correctly estimate a downlink (DL) channel state fromthe eNode B and at the same time can efficiently receive DL data fromthe eNode B.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved with the present invention are not' limitedto what has been particularly described hereinabove and other advantagesof the present invention will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a conceptual diagram illustrating a relay backhaul link and arelay access link for use in a wireless communication system;

FIG. 2 is an exemplary structural diagram illustrating a frame for usein a 3GPP LTE system acting as an exemplary mobile communication systemaccording to an embodiment of the present invention;

FIG. 3 shows a downlink (DL) time-frequency resource grid structure foruse in a 3GPP LTE system acting as an exemplary mobile communicationsystem according to an embodiment of the present invention;

FIG. 4 exemplarily shows a normal subframe structure and a multimediabroadcast multicast service single frequency network (MBSFN) subframestructure for use in a 3GPP LTE system acting as an exemplary mobilecommunication system according to an embodiment of the presentinvention;

FIG. 5 exemplarily shows a backhaul subframe structure of a donor eNodeB (DeNB) and a backhaul subframe structure of a relay node (RN) for usein a 3GPP LTE system acting as an exemplary mobile communication systemaccording to an embodiment of the present invention;

FIG. 6 is a structural diagram illustrating a common reference signal(CRS) structure depending on an antenna port for use in a 3GPP LTEsystem acting as an exemplary mobile communication system according toan embodiment of the present invention;

FIG. 7 exemplarily shows a DRS pattern contained in a single physicalresource block (PRB) of a specific subframe;

FIG. 8 exemplarily shows a PRB structure including not only a CRSpattern of a 3GPP LTE system acting as an exemplary mobile communicationsystem but also a CSI-RS pattern for a relay node (RN);

FIG. 9 exemplarily shows a PRB structure including not only a CRSpattern of a 3GPP LTE system acting as an exemplary mobile communicationsystem but also a CSI-RS pattern for a relay node (RN);

FIGS. 10 and 11 exemplarily show a PRB structure including not only aCRS pattern of a 3GPP LTE system acting as an exemplary mobilecommunication system but also a DM-RS pattern for a relay node (RN);

FIG. 12 shows an example of a PRB structure including not only a CRSpattern of a 3GPP LTE system acting as an exemplary mobile communicationsystem but also a DM-RS pattern for a relay node (RN); and

FIG. 13 is a diagram illustrating constituent elements of an apparatusaccording to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the present invention.The following detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details. For example, thefollowing description will be given centering upon a mobilecommunication system serving as a 3GPP LTE system, but the presentinvention is not limited thereto and the remaining parts of the presentinvention other than unique characteristics of the 3GPP LTE system areapplicable to other mobile communication systems.

In some cases, in order to prevent ambiguity of the concepts of thepresent invention, conventional devices or apparatuses well known tothose skilled in the art will be omitted and be denoted in the form of ablock diagram on the basis of the important functions of the presentinvention. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

In the following description, a user equipment (UE) may refer to amobile terminal, fixed mobile terminal, a mobile station (MS) and thelike. Also, the eNode B (eNB) may refer to an arbitrary node of anetwork end which communicates with the above terminal, and may includea base station (BS), a Node B (Node-B), and an access point (AP) and thelike.

In a mobile communication system, the UE may receive information fromthe eNode B via a downlink, and may transmit information via an uplink.The information that is transmitted and received to and from the UEincludes data and a variety of control information. There are a varietyof physical channels according to categories of transmission (Tx) andreception (Rx) information of the UE.

FIG. 2 is an exemplary structural diagram illustrating a frame for usein a 3GPP LTE system acting as an exemplary mobile communication systemaccording to an embodiment of the present invention.

Referring to FIG. 2, one radio frame includes 10 subframes, and onesubframe includes two slots in a time domain. A time required fortransmitting one subframe is defined as a Transmission Time Interval(TTI). For example, one subframe may have a length of 1 ms and one slotmay have a length of 0.5 ms. One slot may include a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbols or a SingleCarrier Frequency Division Multiple Access (SC-FDMA) symbols in a timedomain.

FIG. 3 shows a downlink (DL) time-frequency resource grid structure foruse in a 3GPP LTE system acting as an exemplary mobile communicationsystem according to an embodiment of the present invention.

Referring to FIG. 3, the 3GPP LTE system is configured to use the OFDMAscheme in downlink. A resource block (RB) is a resource allocation unit.10 subframes may be contained in one radio frame, 2 slots may becontained in one subframe, and 7 OFDM symbols may be contained in oneslot. However, the scope or spirit of the present invention is notlimited thereto and the number of subframes, the number of slots, andthe number of OFDM symbols may also be changed in various ways. Forconvenience of description and better understanding of the presentinvention, the following description assumes that the number of OFDMsymbols contained in one subframe is set to 14.

Referring to FIG. 3, downlink transmission resources can be described bya resource grid including N_(RB) ^(DL)×N_(SC) ^(RB) subcarriers andN_(symb) ^(DL) OFDM symbols. Here, N_(RB) ^(DL) represents the number ofresource blocks (RBs) in a downlink, N_(SC) ^(RB) represents the numberof subcarriers constituting one RB, and N_(symb) ^(DL) represents thenumber of OFDM symbols in one downlink slot. N_(RB) ^(DL) RB varies witha downlink transmission bandwidth constructed in a cell, and mustsatisfy N_(RB) ^(min,DL)≦N_(RB) ^(DL)≦N_(RB) ^(max,DL). Here, N_(RB)^(min,DL) is the smallest downlink bandwidth supported by the wirelesscommunication system, and N_(RB) ^(max,DL) is the largest downlinkbandwidth supported by the wireless communication system. AlthoughN_(RB) ^(min,DL) may be set to 6 (N_(RB) ^(min,DL)=6) and N_(RB)^(max,DL) may be set to 110 (N_(RB) ^(max,DL)=110), the scopes of N_(RB)^(min, UL) and N_(RB) ^(max,UL) are not limited thereto. The number ofOFDM symbols contained in one slot may be differently defined accordingto the length of a Cyclic Prefix (CP) and spacing between subcarriers.When transmitting data or information via multiple antennas, oneresource grid may be defined for each antenna port.

Each element contained in the resource grid for each antenna port iscalled a resource element (RE), and can be identified by an index pair(k,l) contained in a slot, where k is an index in a frequency domain andis set to any one of 0, . . . , N_(RB) ^(DL)N_(sc) ^(RB)−1, and l is anindex in a time domain and is set to any one of 0, . . . , N_(symb)^(DL)−1.

Resource blocks (RBs) shown in FIG. 3 are used to describe a mappingrelationship between certain physical channels and resource elements(REs). The RBs can be classified into physical resource blocks (PRBs)and virtual resource blocks (VRBs).

One PRB is defined by N_(symb) ^(DL) consecutive OFDM symbols in a timedomain and N_(SC) ^(RB) consecutive subcarriers in a frequency domain.N_(symb) ^(DL) and N_(SC) ^(RB) may be predetermined values,respectively. For example, N_(symb) ^(DL) and N_(SC) ^(RB) may be givenas shown in the following Table 1. Therefore, one PRB may be composed ofN_(symb) ^(DL)×N_(SC) ^(RB) resource elements. One PRB may correspond toone slot in a time domain and may also correspond to 180 kHz in afrequency domain, but it should be noted that the scope of the presentinvention is not limited thereto.

TABLE 1 Configuration N_(SC) ^(RB) N_(symb) ^(DL) Normal Δf = 15 kHz 127 Cyclic Prefix Extended Δf = 15 kHz 6 Cyclic Prefix Δf = 7.5 kHz 24 3

The PRBs are assigned numbers from 0 to N_(RB) ^(DL)−1 in the frequencydomain. A PRB number n_(PRB) and a resource element index (k,l) in aslot can satisfy a predetermined relationship denoted by

$n_{PRB} = {\left\lfloor \frac{k}{N_{sc}^{RB}} \right\rfloor.}$The VRB may have the same size as that of the PRB. The VRB may beclassified into a localized VRB (LVRB) and a distributed VRB (DVRB). Foreach VRB type, a pair of PRBs allocated over two slots of one subframeis assigned a single VRB number n_(VRB).

The VRB may have the same size as that of the PRB. Two types of VRBs aredefined, the first one being a localized VRB (LVRB) and the second onebeing a distributed type (DVRB). For each VRB type, a pair of PRBs mayhave a single VRB index (which may hereinafter be referred to as a ‘VRBnumber’) and are allocated over two slots of one subframe. In otherwords, N_(RB) ^(DL) VRBs belonging to a first one of two slotsconstituting one subframe are each assigned any one index of 0 to N_(RB)^(DL)−1, and N_(RB) ^(DL) VRBs belonging to a second one of the twoslots are likewise each assigned any one index of 0 to N_(RB) ^(DL)−1.

FIG. 4 exemplarily shows a normal subframe structure and a multimediabroadcast multicast service single frequency network (MBSFN) subframestructure for use in a 3GPP LTE system acting as an exemplary mobilecommunication system according to an embodiment of the presentinvention.

Referring to the normal subframe of FIG. 4(a), an eNode B may transmitcontrol information over a physical downlink control channel (PDCCH)composed of 1, 2, or 3 OFDM symbols in a single subframe. Therefore, theeNode B may transmit data and/or control information over a physicaldownlink shared channel (PDSCH) composed of the remaining 11, 12, or 13OFDM symbols of the single subframe.

In contrast, referring to the MBSFN subframe of FIG. 4(b), the eNode Bmay transmit a unicast reference signal RS) and a control signal usingone or two OFDM symbols of one subframe, and may transmit MBSFN datausing the remaining 12 or 13 OFDM symbols.

In the following description, a specific zone in which a donor eNBtransmits a control channel (R-PDCCH) for the RN and transmits a datachannel (R-PDSCH) for the RN in a downlink subframe is defined as arelay zone (or relay region). That is, the relay zone is used fordownlink backhaul transmission.

FIG. 5 exemplarily shows a backhaul subframe structure of a donor eNBand a backhaul subframe structure of a relay node for use in a 3GPP LTEsystem acting as an exemplary mobile communication system according toan embodiment of the present invention.

As described above, one subframe may include 14 OFDM symbols. Thedonor-eNB downlink backhaul subframe structure shown in FIG. 5(a) andthe RN backhaul subframe structure shown in FIG. 5(b) are timing-alignedexamples.

Referring to FIG. 5(a), the donor eNB may transmit control informationand the like to UEs and RNs on a PDCCH 510 consist of a predeterminednumber of symbols (e.g., 3 symbols). The donor eNB may transmit dataand/or control information to macro UEs through some regions 520 and 530from among a PDSCH zone. In addition, the donor eNB may transmit controlinformation and/or data to the RN through a zone for the RN (i.e., arelay zone) 540. R-PDCCH acting as a control channel for the RN andR-PDSCH acting as a data channel for the RN may be assigned to the relayzone 540. An idle zone or an LTE-A UE zone 550 may be located next tothe relay zone 540. Provided that the RN downlink subframe shown in FIG.5(b) is time-shifted as compared to the donor-eNB downlink subframeshown in FIG. 5(a) (for example, the RN downlink subframe of FIG. 5(a)is more delayed than the donor-eNB downlink subframe of FIG. 5(a) by apredetermined time corresponding to 0.5 symbol), the idle zone or theLTE-A UE zone 550 may not be assigned.

In the donor-eNB downlink backhaul subframe, the relay zone 540 mayinclude an R-PDCCH zone and an R-PDCCH zone (or region). Therefore, inorder to receive backhaul signal from the donor eNB, there is a need forthe RN to recognize a start point of the R-PDCCH zone and/or a startpoint of the R-PDSCH zone. In the relay zone 540, R-PDCCH and R-PDSCHmay be assigned by frequency division multiplexing (FDM) or timedivision multiplexing (TDM) multiplexed.

Referring to FIG. 5(b), the RN may transmit control information or thelike to the UE over a PDCCH 560 consist of a predetermined number ofsymbols (e.g., one or two symbols). The RN backhaul subframe shown inFIG. 5(b) may be set to a fake-MBSFN subframe for backhaul receptionfrom the donor eNB. In order to switch the RN from a transmission modeto a reception mode, a switching zone is needed. Therefore, a transitiongap 570 may be assigned next to the PDCCH zone 560 corresponding to atransmission zone. In other words, the transition gap 570 may be used asa switching zone. In this case, one OFDM symbol may be assigned to thetransition gap 570. A relay zone 590 in which the RN can receive data,control information, etc. from the donor eNB may be assigned subsequentto the transition gap 570. A transition gap 580 may be assignedsubsequent to the relay zone 590.

The RN has to recognize the R-PDCCH and R-PDSCH start points. TheR-PDCCH and R-PDSCH start points may be determined by the size of the RNPDCCH 560 (e.g., the number of OFDM symbols). For example, it is assumedthat the RN uses two OFDM symbols as a PDCCH zone 560 for UEs. As can beseen from FIG. 5(b), the donor eNB may set the R-PDCCH start pointand/or the R-PDSCH start point to a fourth OFDM symbol. However, if thesize of the RN PDCCH zone 560 is set to one OFDM symbol, a third OFDMsymbol subsequent to the transition gap 570 occupying one OFDM symbolmay be the R-PDCCH and/or R-PDSCH start point(s). In other words, theR-PDCCH and/or R-PDSCH start point(s) may be changed according to thenumber of OFDM symbols corresponding to the PDCCH zone 560 in which theRN can transmit a control signal or the like to a lower UE.

Therefore, irrespective of the number of OFDM symbols (e.g., one or twoOFDM symbols) corresponding to the PDCCH zone 560 in which the RNtransmits a control signal or the like to a lower UE, each of theR-PDCCH and R-PDCCH start points may be fixed to a fourth OFDM symbol,

Information regarding the R-PDCCH and R-PDSCH start points, each ofwhich is fixed to the fourth OFDM symbol, may be signaled from the donoreNB to the RN. Alternatively, each of the R-PDCCH and R-PDSCH startpoints may be previously fixed to the fourth OFDM symbol, such that theRN may implicitly recognize the resultant R-PDCCH and R-PDSCH startpoints. In this case, the donor eNB need not transmit signalinginformation to the RN.

Information regarding the R-PDCCH and R-PDCCH start points of the donoreNB may be transmitted to the RN. Upon receiving the R-PDCCH and R-PDCCHstart point information from the donor eNB, the RN may effectivelyreceive data, control information, etc. from the donor eNB in responseto the relay zone 590 (R-PDCCH and R-PDCCH) timing point. The relay zone590 start point information may indicate the R-PDCCH start point and theR-PDSCH start point.

The above-mentioned relay zone allocation may be cell-specifically orRN-specifically achieved. That is, the donor eNB may cell-specifically(equally to each RN contained in the same cell) allocate the relay zone.In addition, the donor eNB may dynamically assign the relay zone. Forexample, relay zone allocation may be changed per downlink backhaulsubframe. In contrast, the relay zone allocation may besemi-persistently achieved.

A Reference Signal (RS) allocation method and a R-PDCCH constructionmethod for use in the relay zone will hereinafter be described indetail. First, an RS for use in the LTE system and LTE-A system will begiven below.

The RS for use in the LTE system may be classified into a dedicatedreference signal (DRS) and a common reference signal (CRS). The DRS maybe UE-specifically used. Generally, the DRS may be used to demodulatedata or the like. The DRS may be classified into a precoded RS and anon-precoded RS. The CRS may be used for demodulation and channelestimation. All UEs belonging to one cell may share the CRS.

FIG. 6 is a structural diagram illustrating a CRS structure depending onan antenna port for use in a 3GPP LTE system acting as an exemplarymobile communication system according to an embodiment of the presentinvention.

Referring to FIG. 6, CRS patterns of individual antennas may beorthogonal to each other in a time or frequency domain. Provided thatthe LTE system includes one antenna port, CRS may be used as a patternof the antenna port 0. In addition, provided that 4Tx MIMO transmissionis applied to the LTE system, patterns of the antenna ports 0 to 3 maybe simultaneously used as the CRS pattern. In this case, R0 may indicatea CRS of the antenna port 0. In order to minimize interference betweenRSs, other RSs may not be transmitted in the same resource element (RE)for CRS transmission. In addition, a predefined sequence (for example,pseudo-random (PN), etc.) may be multiplexed with a downlink RS so as tominimize the inter-cell interference. As a result, channel estimationthroughput may be improved. The PN sequence may be used as an OFDMsymbol level in one subframe. In this case, the PN sequence may bedefined according to a cell ID, a subframe number, and the location ofan OFDM symbol.

For example, as shown in FIG. 6, the number of RSs in one OFDM symbolthat includes a reference signal (RS) in one RB for each antenna port isset to 2. The number of RBs for use in the LTE system is set to any oneof 6 to 110. Accordingly, a total of RSs for each antenna port in oneOFDM symbol having an RS is denoted by 2×N_(RB). In this case, N_(RB) isthe number of RBs corresponding to a bandwidth, and a sequence may be abinary or complex.

A sequence r(m) may be denoted by a complex sequence.

$\begin{matrix}{{{r(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{m = 0},1,\ldots\mspace{14mu},{{2N_{RB}^{\max}} - 1}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, N_(RB) ^(max) is the number of RBs corresponding to amaximum bandwidth of the LTE system. Therefore, N_(RB) ^(max) may be setto 110 as described above. C is a PN sequence having the length of 31,and may be defined as a Gold sequence. In this case, if a downlink RS isdenoted by a DRS, Equation 1 may also be represented by the followingEquation 2.

$\begin{matrix}{{{r(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{m = 0},1,\ldots\mspace{14mu},{{12N_{RB}^{PDSCH}} - 1}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Equation 2, N_(RB) ^(PDSCH) is the number of RBs allocated to aspecific UE. Therefore, the length of a sequence may be changedaccording to the number of RBs allocated to one UE.

In order to reduce overhead caused by RS transmission, DRS-baseddownlink transmission may be used in the LTE-A system. CRS-baseddownlink transmission always requires RS transmission for all physicalantenna ports. The DRS-based downlink transmission can reduce RSoverhead in consideration of a virtual antenna port requiring an RS. Thenumber of virtual antenna ports may be identical or less than the numberof physical antenna ports. DRS is used for demodulation purpose, suchthat other RSs may be used for channel measurement. Channel stateindicator-reference signal (CSI-RS) may be transmitted according to aduty cycle. As a result, provided that the duty cycle is relatively longenough, the RS overhead may be minimized.

In addition to a common reference signal (CRS) defined in the legacyRelease-8, new RS formats (i.e., DM-RS (Demodulation RS) and CSI-RS)have been introduced to the LTE-A system. DM-RS is an extended versionof the Release-8 UE-specific RS concept for multiple layers. The DM-RSis UE-specifically transmitted, and is transmitted through a scheduledresource block (RB) and the corresponding layer. RSs of individuallayers are orthogonal to each other.

FIG. 7 exemplarily shows a DRS pattern contained in a single physicalresource block (PRB) of a specific subframe.

Referring to FIG. 7, the DRS pattern may support a maximum of 4 layers.Two code division multiplexing (CDM) groups are used to multiplex twolayers in each CDM group, and four layers may be maximally multiplexedusing the above-mentioned pattern. For CDM multiplexing, 2×2 Walshspreading or 4×4 Walsh spreading may be used.

In order to feed back channel status information (CSI) to the donor eNB,there is a need for CSI-RS to be transmitted along with a DRS. The UEand the RN can estimate a downlink channel status using the receivedCSI-RS. CSI-RS may be transmitted in response to a duty cycle (e.g., 5ms). In this case, the duty cycle is set to 5 ms or less.

The donor eNB may transmit the CSI-RS at intervals of a predeterminedtime so as to estimate a downlink channel state of the RN. In this case,CSI-RS may be transmitted in the form of a specific pattern at asubframe of the corresponding period.

Embodiments in which the donor eNB transmits an RS for channel statusmeasurement and demodulation to the RN using a specific pattern willhereinafter be described in detail.

In a downlink backhaul subframe, if the donor eNB transmits at least 4Txantenna transmission scheme (i.e., if the donor eNB supports 5 to 8 Txantennas), there is needed an RS (reference symbol) for enabling the RNto perform channel status measurement and demodulation. In FIGS. 8 to12, R0, R1, R2, R3 are CRSs of antenna ports 0, 1, 2, and 3,respectively.

<Embodiment for Transmitting Reference Signal (RS) to RN

FIG. 8 exemplarily shows a PRB structure including not only a CRSpattern of a 3GPP LTE system acting as an exemplary mobile communicationsystem but also a CSI-RS pattern for a relay node (RN).

In the LTE system, the eNB may transmit the CSI_RS to the Rn through apredetermined downlink backhaul subframe. The RN may perform channelmeasurement and demodulation using the CSI-RS. In this case, the eNB mayassign the CSI-RS to the R-PDCCH zone. In other words, the eNB transmitsthe CSi-RS to the RN through the R-PDCCH zone, resulting in an increaseddecoding performance of a control channel.

Referring to FIG. 8, provided that the eNB transmits a R-PDCCH through Ninitial OFDM symbols of the relay zone, the R-PDCCH can be transmittedto the RN through a first OFDM symbol (i.e., an OFDM symbol having anindex of 3, referred to as a OFDM symbol index 3) depending on the timeorder of the relay zone. In more detail, the first OFDM symbol is afourth OFDM symbol from among 14 OFDM symbols from the OFDM symbol index0 to the OFDM symbol index 13 of the OFDM symbol of the eNB downlinkbackhaul subframe. In this case, the eNB may also transmit the R-PDCCHthrough the first OFDM symbol of the relay zone and a third OFDM symbol(i.e., a OFDM symbol index 5). In other words, the eNB may transmit theR-PDCCH to the RN through the OFDM symbol index 3 and the OFDM symbolindex 5 from among 14 OFDM symbols from the OFDM symbol index 0 to theOFDM symbol index 13 of the OFDM symbol of the eNB downlink backhaulsubframe.

In contrast, the eNB may allocate the CSI-RS to the R-PDCCH zone. Inother words, the eNB may allocate the CSI-RS to the R-PDSCH zone so asto increase a decoding performance of a data channel.

FIG. 9 exemplarily shows a PRB structure including not only a CRSpattern of a 3GPP LTE system acting as an exemplary mobile communicationsystem but also a CSI-RS pattern for the RN.

Referring to FIG. 9, the eNB may assign the CSI-RS to the R-PDCCH zone.That is, the eNB transmits the CSI-RS to the RN through the R-PDCCHregion, resulting in an increased decoding performance of a controlchannel. In the case where the eNB allocates the R-PDCCH to N initialOFDM symbols of a second slot of the relay zone transmits the resultantR-PDCCH, the R-PDCCH may be transmitted to the RN through the last OFDMsymbol (i.e., OFDM symbol index 6) of the first slot. The OFDM symbolindex 6 which is the last OFDM symbol is a 7^(th) OFDM symbol from among14 OFDM symbols from the OFDM symbol index 0 to the OFDM symbol index 0of the OFDM symbol of the eNB downlink backhaul subframe.

In contrast, provided that the eNB transmits the R-PDCCH to N initialOFDM symbols of the second slot, the R-PDCCH may be transmitted to theRN through a third OFDM symbol (i.e., OFDM symbol index 10) of thesecond slot. The OFDM symbol index 10 which is the third OFDM symbol inthe second slot is a 11^(th) OFDM symbol from the OFDM symbol index 0 tothe OFDM symbol index 13 of the OFDM symbol of the eNB downlink backhaulsubframe.

In the meantime, provided that the eNB transmits the R-PDCCH to Ninitial OFDM symbols of the second slot, the R-PDCCH may be transmittedto the RN through the last OFDM symbol of the first slot and the thirdOFDM symbol of the second slot. In other words, the R-PDCCH may betransmitted to the RN through a 7^(th) OFDM symbol (OFDM symbol index 6)and a 11^(th) OFDM symbol (OFDM symbol index 10) among 14 OFDM symbolsof OFDM symbol index 0 to 13 in the eNB downlink backhaul subframe.

Referring to FIG. 9, provided that the R-PCCH is transmitted through Ninitial OFDM symbols of the second slot, the eNB may use a first slot totransmit a PDSCH of an LTE-A UE for a macro cell or to transmit aR-PDSCH for the RN.

In this case, a size of the OFDM symbol (N OFDM symbol) used for R-PDCCHtransmission may be semi-statically assigned. The eNB may signal the Nvalue to the RN through higher layer signaling or a broadcast channel.In contrast, the N OFDM symbol used for R-PDCCH transmission may bedynamically changed per backhaul subframe. In this case, arelay-physical control format indicator channel (R-PCFICH) is assignedto the R-PDCCH zone, such that the eNN may signal the N value to the RNthrough the R-PCFICH.

The position of a control channel for the RN may be located at the fifthOFDM symbol (i.e., OFDM symbol index 4) shown in FIG. 8. In this case,the control channel can be decoded using the legacy CRS (R0 and R1)without using the CSI-RS. Although R0 and R1 can be used irrespective ofthe location of a control channel for the RN, if the control channel forthe RN is shifted to the fifth OFDM symbol, the fourth OFDM symbol maybe used as a PDSCH for the RN, a PDSCH for LTE-A, or other controlchannels.

If the RN uses the CSI-RS for demodulation, this CSI-RS and the legacyCRS may be used interchangeably. That is, R0 and R1 present at the fifthOFDM symbol are used as two antenna ports, and the remaining necessaryantnea ports may be extracted from CSI-R. In contrast, as shown in FIG.9, if a control channel is present in the first part of the second slot,a method for reusing CRS ports R0 to R3 may be used. In this case, theremaining necessary channels may be extracted from the CSI-RS.

A MIMO mode contained in a control channel for the RN may include aspatial multiplexing mode and a diversity mode. In this case, the numberof necessary antenna ports may be limited to 2 or 4. In this case, thenumber of types of necessary reference symbols (reference signals) islimited to 2 or 4. Such limitation may be implemented only using theCRS. In other words, as a method for decoding control information forthe RN, a method for defining the spatial multiplexing mode or diversitymode without using the CSI-RS and DRS may be used. Here, the CSI-RSposition may be located at an arbitrary position irrespective of the RNcontrol channel.

The RN control channel may define a MIMO mode according to new antennaport definition based on an arbitrary combination of the CSI-RS. Inother words, CSI-RS for all the antennas is defined as Rank 1, precodingmay be applied to the control channel such that the precoded result canbe transmitted. If the diversity mode is defined, a control channel isdivided into arbitrary groups, precoding is applied to individualgroups, such that the precoded result can be transmitted. If the spatialmultiplexing mode is defined, precoding may be applied to each groupedantenna and at the same time a spatial stream for each antenna group maybe defined. In this case, the legacy CRS instead of the used CSI-RS maybe used as necessary.

FIGS. 10 and 11 exemplarily show a PRB structure including not only aCRS pattern of a 3GPP LTE system acting as an exemplary mobilecommunication system but also a DM-RS pattern for a relay node (RN).

A dedicated reference signal (DRS) acting as a demodulation referencesignal for RNs in a relay zone of a backhaul subframe is defined, andthe RN performs channel measurement and demodulation using the definedDRS. The OFDM symbol position at which the DRS is assigned andtransmitted may be identical to an OFDM symbol position at which theCSI-RS is assigned and transmitted. For example, as can be seen fromFIGS. 10 and 11, DRS may be assigned to the OFDM symbol having an indexof 3 or 9.

FIG. 12 shows an example of a PRB structure including not only a CRSpattern of a 3GPP LTE system acting as an exemplary mobile communicationsystem but also a DM-RS pattern for a relay node (RN).

Referring to FIG. 12, RSs corresponding to antenna ports 4 to 8 may betransmitted through one or more OFDM symbols from among OFDM symbolindexes 3, 5, 6, 9, 10 and 12 at the same frequency position as those ofFIGS. 10 and 11 (i.e., the frequency position corresponding to asubcarrier index at which DRS is assigned in FIGS. 10 and 11). If DRSfor the RN is transmitted through a plurality of OFDM symbols, frequencyhopping of an RS corresponding to a port in response to an OFDM symbolmay be achieved as shown in FIG. 12.

If DRS is applied to control channel demodulation, precoding may beapplied to DRS. In this case, different precoding methods may be appliedto a DRS of a control channel region and a DRS of a data region.However, from the standpoint of channel estimation facility and RSdesign, the control channel DRS is identical to the data channel DRS,and precoding may be applied to each DRS or a MIMO mode may be definedsuch that the resultant data may be transmitted. In this case, there isa need for the order of channel estimation requisite for the controlchannel to be identical to a data estimation order of the data channel.That is, although the diversity mode is applied to the control channeland the spatial multiplexing mode is applied to the data channel, thereis a need for the number of channel estimation times requisite for thecontrol channel region to be identical to that of the data region.

A unit for generating a control channel for the RN may be identical to adata allocation unit. In other words, provided that the number of RBsused in the control channel is set to A, the number of RBs of the datachannel indicated by the corresponding control channel must be set to Aor higher. By such allocation, a DRS of the control channel and a DRS ofthe data channel can be equally precoded. In association with a specificpart at which no control channel is allocated, DRS may be precoded inthe same manner as in precoding of a data channel allocated to aspecific RN.

For the control channel for the RN, a new control channel dedicated RSmay be defined as necessary. In case of a DRS for the data channel, ifeither the number of DRS allocations or density is insufficient, it isexpected that performance is deteriorated due to the control channel. Inorder to obviate the performance deterioration, a separate RS may bedefined in an assignment region of the RN control channel. In case ofthe RN control channel, the amount of used resources may be limited,such that the remaining region may be used as an RS for the controlchannel and the RS may be defined as a 1Tx, 2Tx, 4Tx, or 8Tx structurein response to a transmission mode used in the control channel. Inaddition, the remaining region obtained after the control channel and RSare used may be still utilized as data for the RN. In this case,although demodulation of the data part may be used as an RS for thecontrol channel, it should be noted that the data part demodulation maybe achieved on the basis of the DRS for the RN data region.

As another embodiment for enabling the eNB to transmit an RS to the RN,there may be used a method for allocating the CSI-RS in the LTE-A systemand allocating a DRS in a relay zone in such a manner that the RN canperform channel estimation and demodulation using two RSs.

A R-PDCCH format for the RN will hereinafter be described in detail. TheeNB may transmit scheduling allocation information, other controlinformation, etc. to the Rn over the R-PDCCH. A physical control channeltransmitted from the eNB to the RN may be transmitted through oneaggregation or plurality of contiguous control channel elements (CCEs).In this case, one CCE may include 9 resource element (RE) groups.

In the R-PDCCH format acting as the RN control. channel, QuadraturePhase Shift Keying (QPSK) or 16 Quadrature Amplitude Modulation (QAM),64QAM, etc. may be used as a modulation scheme. The size of resourceelement modulation (REG) may correspond to four contiguous REs that arenot used as RS, R-PCFICH (Relay-Physical Control Format IndicatorChannel), and R-PHICH (Relay-Physical HARQ Indicator Channel). The sizeof 9 REG CCEs may be maintained irrespective of the modulation scheme.The number of R-PDCCH bits may be determined according to a modulationscheme and a CCE aggregation level.

For example, in case of R-PDCCH format 0, CCE aggregation level is setto 1 and the number of R-PDCCH bits may be determined according to eachmodulation scheme. In case of the QPSK, information of 72 bits may beassigned to R-PDCCH format 0, information of 144 bits may be assigned to16QAM, and information of 216 bits may be assigned to 64QAM.

The R-PDCCH format according to the CCE aggregation level may have thesame structure as that of the PDCCH format of the LTE system. In otherwords, aggregation levels 1, 2, 4 and 8 may be maintained irrespectiveof the modulation scheme. The R-PDCCH format may support an aggregationlevel of 8 or higher as necessary. In this case, a search space of theRN may also be decided, in response to the supported aggregation level.For example, the search space of the RN may support aggregation levels16, 32, . . . .

Irrespective of the modulation scheme, the number of R-PDCCH bitscorresponding to one CCE may be maintained (for example, 1 CCE=72 bits).In this case, the CCE size depending on one modulation scheme can bedetermined as follows. For example, the QPSK scheme may have the size of9 REG CCEs, the 16QAM may have the size of 4.5 REG CCEs, and the 64QAMmay have the size of 3 REG CCEs. Irrespective of the modulation scheme,the CCE aggregation level constructing one R-PDCCH may be maintained at1, 2, 4, and 8 as in the ITE system. Irrespective of the modulationscheme, the CCE aggregation level constructing one R-PDCCH may be set to1, 2, 4 and 8 or new aggregation levels of 16, 32, 64, . . . may beapplied as necessary.

The same modulation scheme may be applied to R-PDCCHs of a predeterminedbackhaul subframe.

The R-PDCCH modulation scheme may be semi-statically determined. In thiscase, the R-PDCCH modulation scheme may be transmitted to each RNthrough higher layer signaling. Alternatively, the eNB may dynamicallychange the R-PDCCH modulation scheme at every subframe, such that thechanged information may be used as broadcast information for each RN. Inanother example, the eNB may explicitly inform the RN of the R-PDCCHmodulation scheme over the R-PCFICH, and the eNB may implicitly indicatethe R-PDCCH modulation scheme. For example, the same modulation schemeas that of the R-PCFICH may also be applied to the R-PDCCH.

In a predetermined backhaul subframe, different modulation schemes maybe applied to individual R-PDCCHs. In this case, the RN may beconfigured to perform blind search in response to all modulationschemes.

The mapping of R-PDCCH to CCE RE may be carried out in the same manneras in the mapping scheme of the LTE system. In order to implementR-PDCCH transmission when data is assigned to a cell-specific relayzone, a transmission diversity (TxD) scheme depending on the antennastructure may be used. In the case where data is assigned to theRN-specific relay zone, the transmission diversity scheme or theprecoded beamforming may be used to implement R-PDCCH transmission.

FIG. 13 is a diagram illustrating constituent elements of a device 50,which is applicable to a user equipment (UE) or an eNode B and is ableto implement embodiments of the present invention.

Referring to FIG. 13, a device 50 may be a user equipment (UE) or aneNode B (eNB). The device 50 includes a processor 51, a memory 52, aRadio Frequency (RF) unit 53, a display unit 54, and a user interfaceunit 55.

Layers of the radio interface protocol are implemented in the processor51. The processor 51 provides a control plane and a user plane. Theprocessor 51 may perform functions of each layer. The memory 52, whichis electrically connected to the processor 51, stores an operatingsystem, application programs, and general files.

The display unit 54 may display various pieces of information and beconfigured with a Liquid Crystal Display (LCD), an Organic LightEmitting Diode (OLED), etc. which are known in the art.

The user interface unit 55 may be configured to be combined with a knownuser interface such as a keypad, a touch screen, or the like.

The RF unit 53, which is electrically connected to the processor 51,transmits and receives RF signals. The RF unit may be classified into aprocessor transmission (Tx) module (not shown) and a processor reception(Rx) module (not shown).

Radio interface protocol layers between the UE and a network can beclassified into a first layer (L1 layer), a second layer (L2 layer) anda third layer (L3 layer) on the basis of the lower three layers of theOpen System Interconnection (OSI) reference model widely known incommunication systems. A physical layer belonging to the first layer(L1) provides an information transfer service through a physicalchannel. A Radio Resource Control (RRC) layer belonging to the thirdlayer (L3) controls radio resources between the UE and the network. TheUE and the network may exchange RRC messages with each other through theRRC layer.

Exemplary embodiments described hereinbelow are combinations of elementsand features of the present invention. The elements or features may beconsidered selective unless otherwise mentioned. Each element or featuremay be practiced without being combined with other elements or features.Further, an embodiment of the present invention may be constructed bycombining parts of the elements and/or features. Operation ordersdescribed in embodiments of the present invention may be rearranged.Some constructions of any one embodiment may be included in anotherembodiment and may be replaced with corresponding constructions ofanother embodiment. Also, it will be obvious to those skilled in the artthat claims that are not explicitly cited in the appended claims may bepresented in combination as an exemplary embodiment of the presentinvention or included as a new claim by subsequent amendment after theapplication is filed.

The embodiments according to the present invention can be implemented byvarious means, for example, hardware, firmware, software, orcombinations thereof. If the embodiment according to the presentinvention is implemented by hardware, the embodiment of the presentinvention can be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

If the embodiment according to the present invention is implemented byfirmware or software, the embodiment of the present invention may beimplemented by a type of a module, a procedure, or a function, whichperforms functions or operations as described above. Software code maybe stored in a memory unit and then may be driven by a processor. Thememory unit may be located inside or outside the processor to transmitand receive data to and from the processor through various means whichare well known.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

INDUSTRIAL APPLICABILITY

A method for receiving a signal at the RN according to embodiments ofthe present invention can be applied to various mobile communicationsystems, for example, 3GPP LTE system, LTE-A, and other systems.

The invention claimed is:
 1. A method for receiving a signal by a relaynode in a wireless communication system, the method comprising:receiving information regarding a start point of a relay-physicaldownlink control channel (R-PDCCH) at a specific downlink subframeconfigured for an eNode B-to-the relay node transmission, wherein thestart point of the R-PDCCH is a fourth orthogonal frequency divisionalmultiplexing (OFDM) symbol in the specific downlink subframe; receivingthe R-PDCCH during the fourth OFDM symbol to a sixth OFDM symbol of thespecific downlink subframe based on the information regarding the startpoint of the R-PDCCH; demodulating the R-PDCCH based upon a referencesignal for demodulation transmitted on an antenna port 7; and receivinga data channel for the relay node based upon the R-PDCCH, wherein thereference signal is mapped to a resource element in a first slot of thespecific downlink subframe when a last symbol of the data channel is asixth OFDM symbol of the second slot of the specific downlink subframe.2. The method according to claim 1, wherein the information regardingthe start point of the R-PDCCH is received through a higher layersignaling from the eNode B.
 3. A relay node for receiving a signal in awireless communication system, the relay node comprising: a radiofrequency (RF) unit that: receives information regarding a start pointof a relay-physical downlink control channel (R-PDCCH) at a specificdownlink subframe configured for an eNode B-to-the relay nodetransmission, wherein the start point of the R-PDCCH is a fourthorthogonal frequency divisional multiplexing (OFDM) symbol in thespecific downlink subframe, and receives the R-PDCCH during the fourthOFDM symbol to a sixth OFDM symbol of the specific downlink subframebased on the information regarding the start point of the R-PDCCH, and aprocessor that demodulates the R-PDCCH based upon a reference signal fordemodulation transmitted on an antenna port 7, and wherein the radiofrequency (RF) unit receives a data channel for the relay node basedupon the R-PDCCH, wherein the reference signal is mapped to a resourceelement in a first slot of the specific downlink subframe when a lastsymbol of the data channel is a sixth OFDM symbol of the second slot ofthe specific downlink subframe.
 4. The relay node according to claim 3,wherein the information regarding the start point of the R-PDCCH isreceived through a higher layer signaling from the eNode B.
 5. A methodfor transmitting a signal by an eNode B in a wireless communicationsystem, the method comprising: configuring a start point of arelay-physical downlink control channel (R-PDCCH) at a specific downlinksubframe configured for the eNode B-to-a relay node transmission;transmitting information regarding the start point of the R-PDCCH,wherein the start point of the R-PDCCH is a fourth orthogonal frequencydivisional multiplexing (OFDM) symbol in the specific downlink subframe;modulating the R-PDCCH based upon a reference signal for demodulation tobe transmitted on an antenna port 7; transmitting the R-PDCCH during thefourth OFDM symbol to a sixth OFDM symbol of the specific downlinksubframe based on the information regarding the start point of theR-PDCCH; and transmitting a data channel for the relay node based uponthe R-PDCCH, wherein the reference signal is mapped to a resourceelement in a first slot of the specific downlink subframe when a lastsymbol of the data channel is a sixth OFDM symbol of the second slot ofthe specific downlink subframe.
 6. An eNode B for transmitting a signalin a wireless communication system, the eNode B comprising: a processorthat configures a start point of a relay-physical downlink controlchannel (R-PDCCH) at a specific downlink subframe configured for theeNode B-to-a relay node transmission; and a radio frequency (RF) unitthat transmits information regarding the start point of the R-PDCCH,wherein the start point of the R-PDCCH is a fourth orthogonal frequencydivisional multiplexing (OFDM) symbol in the specific downlink subframe;wherein the processor modulates the R-PDCCH based upon a referencesignal for demodulation to be transmitted on an antenna port 7, andwherein the radio frequency (RF) unit: transmits R-PDCCH during thefourth OFDM symbol to a sixth OFDM symbol of the specific downlinksubframe based on the information regarding the start point of theR-PDCCH, and transmits a data channel for the relay node based upon theR-PDCCH, wherein the reference signal is mapped to a resource element ina first slot of the specific downlink subframe when a last symbol of thedata channel is a sixth OFDM symbol of the second slot of the specificdownlink subframe.